1. Field of the Invention
This invention relates to an apparatus including a fuel cell and a generator for powering a load, and in particular, to such an apparatus which provides a reconfigurable direct current voltage-current profile for a unipolar or homopolar motor from selected solid oxide fuel cell sub-modules and from selected generator armature turns.
2. Background of Information
Mechanical propulsion systems for mobile machines have evolved over the past two centuries. For example, early steamboats were direct replacements for rowboats and sailboats. Other initial propulsion systems upgraded or replaced previous animal propulsion systems. Early steam railway engines, for example, were essentially replacements for horsepower. Today, in developed nations, draft animals are primarily merely historical curiosities.
Automotive engines, for example, typically evolved from stationary engine types as stationary engine technology grew in capabilities and offered improved performance parameters. Improvements in fuel efficiency, powerplant specific weight and space, fixed and operating costs, reliable operation, and ease of operation have been the most important motivating factors in automotive power applications. The predominance of steam, electric, gasoline, diesel, and gas turbine engines has waxed and waned depending on the fixed cost of the engine, the variable operating cost of the fuel, the amount of pollution caused by the fuel (i.e., the environmental cost), and the ability of the various engine manufacturers to compete in the marketplace. This economics-driven turbulence continues to govern the engine industries today.
It is well-known to use a battery to power an electric motor which propels a vehicle. In a land vehicle, for example, a power electronic controller is typically used to control a traction motor in response to a driver's demand. However, such controller includes fixed losses in the primary power control loop and, hence, there is room for reduction of the resulting power losses.
The major difference between conventional electric vehicles and conventional internal combustion vehicles is the energy storage mechanism (i.e., a battery in place of a liquid fuel such as gasoline) and the engine (i.e., an electric motor including a power electronic controller in place of an internal combustion engine). From an environmental standpoint, the use of batteries, which provide "zero emissions", is preferred over liquid fuels, which typically generate hydrocarbon and other pollutants. Nevertheless, batteries merely move the source of the pollution from the vehicle to an electric utility which produces the electricity to recharge the batteries.
Although internal combustion engines generate pollutants and are inefficient, energy can be conveniently stored in reasonable quantities in the vehicle and is readily available on demand. Furthermore, such vehicle can be conveniently and quickly refueled. On the other hand, batteries are inherently limited in terms of both operating range and recharge rate. For example, the energy density (i.e., energy per unit weight or volume) of conventional lead-acid batteries is about 40 WH/Kg compared to the energy density of gasoline of about 12,000 WH/Kg.
Fuel cells are also well-known in the art. Examples of fuel cells are discussed in J. H. Hirschenhofer et al., Fuel Cells A Handbook (Revision 3), dated January 1994, U.S. Department of Energy, publication DOE/METC-94/1006 (DE94004072), which is incorporated herein by reference. Fuel cells are energy conversion devices which produce heat and direct current (DC) electricity from a chemical fuel and an oxidizer through a continuous electrochemical reaction.
Technological combinations of simpler engine types have been provided in order to achieve the advantages and, also, avoid the disadvantages of such engine types. In this light, turbo-charged diesel engines successfully retain the efficiency of naturally-aspirated diesels while overcoming some of their weight penalties. Other compound engines have also been built, including hybrid electric/combustion configurations.
It is further known to provide a hybrid vehicle which utilizes a high energy density device (e.g., a liquid fuel or a fuel cell) in conjunction with a high power density (i.e., power per unit weight or volume) device (e.g., a battery and/or a flywheel). The high energy density device provides an average or baseline power. In contrast, the high power density device furnishes peak power for acceleration and/or climbing hills. The efficiency gains result from improved operating points which reduce both fuel consumption and total exhaust emissions. In maritime vehicles, for example, there is no strict requirement for rapid acceleration and, thus, the power density requirement is less demanding. On the other hand, in land vehicles, where rapid acceleration and hill climbing are needed, a relatively high power density is required.
It is generally well recognized that a satisfactory solution to the energy storage functional requirement is the major technological barrier to a practical electrical vehicle. Efficient, economical, lightweight electric motors and compatible drive systems are evolving to meet specific drive application needs. While a DC motor used to be the primary solution, alternating current (AC) motors appear to be the motor of choice at the present time. This is because the AC motor is both simpler (lower cost) and is capable of much higher rotational speeds than the (conventional or traditional) DC motor, even though the required AC motor control is much more complex (e.g., a simple chopper is all that is typically required for the DC motor).
When both the control system and the machine are considered, some experts believe that there is little fundamental difference in the AC or (conventional) DC drives. The (traditional) DC machine is an almost ideal traction motor, but is expensive. Also, due to the speed limitations of the (traditional) DC machine, it must be larger than an AC machine for an equivalent power requirement. Using sophisticated, complex power electronics, the low cost AC machine can be made to behave like a DC traction machine.
There is a need, therefore, for an improved electric vehicle.
More particularly, there is a need for such a vehicle that utilizes common fuels.
There is another more particular need for such a vehicle that has an improved operating range.
There is still another more particular need for such a vehicle that has an improved capability for acceleration.
There is yet another more particular need for such a vehicle that significantly reduces net total pollution.
There is a further more particular need for such a vehicle that reduces fixed and operating costs.